Hybrid lighter-than-air vehicle

ABSTRACT

The present invention is a variable geometry lighter-than-air (LTA) aircraft that is adapted to morph its shape from a symmetric cross-section buoyant craft to an asymmetric lifting body and even to a symmetric zero lift configuration. The basic structure is a semi rigid airship with movable longerons. Movement of the longerons adjusts the camber of the upper and/or lower surfaces to achieve varying shapes of the lifting-body. This transformation changes both the lift and drag characteristics of the craft to alter the flight characteristics. The transformation may be accomplished while the craft is airborne and does not require any ground support equipment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, generally, to aircrafts. More specifically, it relates to aircrafts convertible between lighter-than-air and heavy-than-air configurations.

2. Brief Description of the Prior Art

Lighter-Than-Air (LTA) aircrafts have some characteristics not shared with Heavier-Than-Air (HTA) aircrafts in that they can maintain altitude without moving in the medium and can do so as long as buoyancy is maintained. LTA aircraft uses low-density gas, such as helium or hydrogen to float in the higher density air. These aircrafts usually employ one or more gasbags filled with the low-density gas to create a buoyancy force that offsets the weight of the aircraft. The downside is that LTA aircrafts are large in size, which is accompanied by large drag characteristics, preventing them from traveling at higher speeds. The current record speed for an LTA aircraft is 112 Km/hr (69.6 mph).

HTA aircrafts use Newton's third law and Bernoulli's principle to achieve flight. HTA crafts generally are either fixed wing or rotor wing aircraft. In either case, part or parts of the structure (e.g., wing, rotors, propellers, fuselage, and control surfaces) have a characteristic shape called an airfoil. Airfoils are generally asymmetric in cross-section with the distance across the upper surface longer than the distance across the lower surface. This causes air moving across the upper surface to travel faster than that traveling across the lower surface causing the pressure on the upper surface to decrease resulting in lift. Lift can also be altered for an airfoil by altering the angle of attack (AoA) relative to the oncoming airflow. Increased AoA causes mass deflection resulting in lift (Newton's third law). Generally, increasing AoA increases lift to an angle at which the airflow separates from the surface of the airfoil causing a condition of aerodynamic stall (at which lift decreases abruptly).

Regardless of how lift is created, an HTA requires a wing-like structure moving through a fluid. Movement requires a power source and no power source is indefinite. Therefore, the HTA aircrafts can only maintain flight for limited periods of time. Even powerless gliders have duration limits as they trade airspeed for altitude gained from thermal lift. However, one of the benefits includes low drag characteristics and thus, high-speed flight.

Any body traveling through a fluid (air in this case) also interacts with the air molecules creating both friction and turbulence, resulting in aerodynamic drag. For a fixed wing aircraft to fly, (change attitude and altitude in the fluid medium) a balance of forces must be achieved with the thrust (motive force of the body through the medium) exceeding the drag and lift exceeding the force of gravity.

The clear tradeoff between LTA and HTA aircrafts is speed verse indefinite flight. The added benefit of an LTA to hover, or station-keep, for extended periods is a significant capacity for observation or surveillance roles. The ideal aircraft would include both indefinite flight and high speed capabilities. This can theoretically be achieved through an aircraft convertible between an LTA and an HTA configuration. Currently, there exist hybrid convertible aircrafts, but none that provide a unique combination of attributes of both a fixed wing aircraft and a LTA craft allowing indefinite mission durations, low energy station keeping, and the ability to dash at relatively high velocities.

U.S. Pat. No. 5,005,783 to James D. Taylor teaches a variable geometry airship capable of converting between a LTA and HTA airship. However, the airship is operationally complex and does not extend the operating range sufficiently to be practical as shown in Table 1. Along with multiple other pitfalls, the shape and design of this airship prevents the airship from transforming into both a symmetric neutral lift configuration and a negative lift configuration, thereby reducing the effectiveness of the airship.

U.S. Pat. No. 4,102,519 to Edward L. Crosby, Jr. teaches a variable lift inflatable airfoil. However, this invention lacks internal moveable structures, which prevent the airfoil from achieving multiple configurations. Additionally, the airfoil lacks a propulsion system and control surfaces.

Accordingly, what is needed is an improved variable geometry aircraft having simple, moveable internal structure to easily convert the aircraft between a lighter-than-air configuration and a heavier-than-air configuration. However, in view of the art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the field of this invention how the shortcomings of the prior art could be overcome.

All referenced publications are incorporated herein by reference in their entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicant in no way disclaims these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein.

The present invention may address one or more of the problems and deficiencies of the prior art discussed above. However, it is contemplated that the invention may prove useful in addressing other problems and deficiencies in a number of technical areas. Therefore, the claimed invention should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein.

In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.

BRIEF SUMMARY OF THE INVENTION

The long-standing but heretofore unfulfilled need for an improved variable geometry aircraft having simple, moveable internal structure to easily convert the aircraft between a lighter-than-air configuration and a heavier-than-air configuration is now met by a new, useful, and nonobvious invention.

The novel structure includes a convertible design having a lighter-than-air configuration and a heavier-than-air configuration along with a propulsion system and a flexible envelope enclosing a base structure, moveable longerons, and length-adjusting envelope expansion arms.

The base structure includes a central core running along a central longitudinal axis of the aircraft, a leading edge strut extending in a direction perpendicular to and in communication with the central core, a trailing edge strut extending in a direction perpendicular to and in communication with the central core, a port side outrigger extending in a direction parallel to the central core and in communication with struts, and a starboard side outrigger extending in a direction parallel to the central core and in communication with struts. Additionally, the base structure is in communication with the moveable longerons and the envelope expansion arms.

The moveable longerons include upper and lower longerons. The upper longerons are in communication with the flexible envelope and an upper translation assembly. The upper translation assembly has an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the upper moveable longerons are in a low camber orientation. In transitioning to the retracted configuration, the upper translation assembly pulls the upper moveable longerons inward towards the central longitudinal axis of the aircraft to decrease aircraft thickness. In transitioning to the extended configuration, the upper translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the upper moveable longerons in a more vertical orientation, which increases the aircraft thickness, compared to longeron's orientation in the retracted configuration.

Similarly, the lower longerons are in communication with the flexible envelope and a lower translation assembly. The lower translation assembly has an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the lower moveable longerons are in a low camber orientation. In transitioning to the retracted configuration, the lower translation assembly pulls the lower moveable longerons inward towards a central longitudinal axis of the aircraft to decrease aircraft thickness. In transitioning to the extended configuration, the lower translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the lower moveable longerons in a more vertical orientation, which increases the aircraft's thickness, compared to longeron's orientation in the retracted configuration.

The upper and lower moveable longerons each include a port side longeron and a starboard side longeron, wherein each longeron has a generally arc shape and a predetermined length that extends in generally the same direction as the central longitudinal axis of the aircraft. Moreover, the moveable longerons are in a generally vertical orientation when in the high camber position and in an acute angle orientation when in the low camber position.

The length-adjusting envelope expansion arms comprise of a port side envelope expansion arm and a starboard side envelope expansion arm. Each arm has a generally arc shape, is subjected to a bias force attempting to force each arm in a direction away from the central longitudinal axis of the aircraft resulting in an increased arc shape, and is in communication with the flexible envelope. Additionally, each envelope expansion arm has a retracted position and an expanded position, where in the retracted position, the length and arc of the envelope expansion arm is at a minimum and in the expanded position, the length and arc of the envelope expansion arm is at a maximum. The retracted position is achieved when a tension force in the flexible envelope overcomes the bias force, resulting from the transition of the moveable longerons towards a more vertical orientation, thereby reducing the length and arc of the envelope expansion arm. Contrastingly, the expanded position is achieved when the tension force in the flexible envelope is overcome by the bias force, resulting from the transition of the moveable longerons to a more horizontal orientation, thereby increasing the length and arc of the envelope expansion arm. Due to the positioning of the envelope expansion arms, the span of the aircraft is directly affected by the transition between the retracted position and the extended position.

In a certain embodiment, the envelope expansion arm is an anisotropic beam having two or more composite rods with cross members extending between the rods. The cross members are designed to have a predetermined spring constant embedded into the structure. One of the composite rods is pivotally attached to the aircraft and one or more of the composite rods are anchored against the pivot structure to provide a source of the tension.

The novel structure further includes a structural connection point to connect the base structure with the moveable longerons and the envelope expansion arms. The structural connection point has a first fixed connection attached to an outrigger, a second fixed connection attached to a strut, a first pivoting connection attached to one of the upper moveable longeron, a second pivoting connection attached to one of the lower moveable longeron, and a third pivoting connection attached to one of the envelope expansion arms.

Moreover, the aircraft uses a gas storage and retrieval system adapted to house, distribute, and retrieve lighter-than-air gas. This system allows the aircraft to easily convert between a lighter-than-air configuration and a heavier-than-air configuration multiple times without having to refill on gas. Furthermore, the aircraft has a propulsion system that includes an electrical generator system adapted to convert wind energy into electrical energy while the aircraft is in the lighter-than-air configuration. In a certain embodiment, flexible solar panels are attached to an exterior surface of the envelope to retrieve and convert solar energy into electrical energy to extend mission time. In addition, the aircraft has a payload hard point attached to the lower translation assembly to facilitate the attachment and management of external payloads in addition to payloads attached internally to the core structure.

These and other important objects, advantages, and features of the invention will become clear as this disclosure proceeds.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the disclosure set forth hereinafter and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a certain embodiment of the present invention in an LTA configuration.

FIG. 2 is a perspective view of an embodiment of the present invention in a negative lift configuration.

FIG. 3 is a side view of an embodiment of the present invention shown in a positive lift configuration.

FIG. 4A is a side view of the present invention in an LTA configuration.

FIG. 4B is a front view of the present invention in an LTA configuration.

FIG. 5A is a side view of the present invention in the dash configuration.

FIG. 5B is a perspective view of the present invention in the dash configuration.

FIG. 5C is a front view of the present invention in the dash configuration.

FIG. 6 is a captured output for a symmetric air foil with high thickness as a percentage of chord that was achieved using FoilSim software.

FIG. 7 is a captured output for a symmetric air foil with low thickness as a percentage of chord that was achieved using FoilSim software.

FIG. 8 is a captured output for an asymmetric air foil with low thickness as a percentage of chord that was achieved using FoilSim software.

FIG. 9 is a perspective view of a certain embodiment of the present invention illustrating the location of reinforcement layers.

FIG. 10 is a perspective view of a certain embodiment showing the configuration of internal panels used to create compartmentalized gas bladders.

FIG. 11 is a perspective view of a certain embodiment of the present invention showing the internal structural components of the aircraft.

FIG. 12 is a rear perspective view of the starboard side of a certain embodiment of the present invention showing the internal structural components of the aircraft.

FIG. 13 is an exploded view of a certain embodiment of a structural connection point.

FIG. 14A is a top view of the internal base structure of a certain embodiment of the present invention.

FIG. 14B is a top view of the internal base structure of a certain embodiment of the present invention shown in a folded configuration.

FIG. 15 is a certain embodiment of the envelope expansion arm.

FIG. 16 is a perspective view of a certain embodiment of the upper translation assembly.

FIG. 17A is front view of a certain embodiment of the upper translation assembly in an extended configuration.

FIG. 17B is front view of a certain embodiment of the upper translation assembly in a retracted configuration.

FIG. 18 is a front view of a certain embodiment of the lower translation assembly, having a payload hard point, while in an extended orientation.

FIG. 19 is a top view of FIG. 18.

FIG. 20 is a front view of the lower translation assembly shown in FIG. 18 while in a retracted orientation.

FIG. 21 is a bottom view of FIG. 20.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form a part thereof, and within which are shown by way of illustration specific embodiments by which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.

GLOSSARY OF CLAIM TERMS

Envelope: is a lightweight flexible material.

Heavier-Than-Air Configuration: is a configuration of the aircraft that cannot maintain altitude without moving in the medium or changing the angle of attack.

Lighter-Than-Air Configuration: is a configuration of the aircraft that can maintain altitude without moving in the medium.

Longeron: is a structural member of the aircraft.

Outrigger: is a rod or bar forming part of a framework and designed to resist compression that extends in generally the same direction as the longitudinal axis of the aircraft.

Payload Hard Point: is an attachment point for payloads or instruments carried on the aircraft.

Propulsion System: is a system capable of moving the aircraft through a medium.

Strut: is a rod or bar forming part of a framework and designed to resist compression.

The present invention is a variable geometry aircraft capable of morphing its shape from a buoyant craft having a symmetric cross-section to an asymmetric lifting body configuration or to a low camber symmetric shape. The convertibility of the present invention provides a unique combination of attributes of both a fixed wing aircraft and a LTA aircraft allowing indefinite mission durations, low energy station keeping and the ability to dash at relatively high velocities (the term “dash” herein refers to this high speed mode where the aircraft has a symmetric zero lift configuration). Additionally, the aircraft is highly portable by folding into a transportable configuration, relatively silent in operation, low cost to produce and operate, and has a unique structure that allows it to operate even if the gas envelope is penetrated. Although there are numerous other aircraft technologies, this device can operate across a number of operating envelopes and perform multiple roles very well without significant compromise (See Table 1 below). This ability is facilitated by the unique internal structural elements of the aircraft.

TABLE 1 Table 1: Aircraft Comparison Velocity Range Operating Operational Aircraft (kts) Cost Complexity Duration Rotor/VTOL 0-115 (217*) High High Low Fixed Wing 50+ Low-High Low-Med Low LTA 0-30 (60*) Low Low-Med High Hybrid LTA** 0-40 High High Med Present 0-200 Low Low High Invention *World Record **Only viable recorded device defined in U.S. Pat. No. 5,005,783

Table 1 above illustrates that the present invention fills a unique performance niche in that, with low complexity and highly reliable, a unique and broad range of performance feats can be achieved (Note: VTOL stands for vertical takeoff and landing). Furthermore, other Hybrid LTAs (e.g., U.S. Pat. No. 5,005,783) are too operationally complex, and do not extend the operating range sufficiently to be practical. No such designs have ever proceeded beyond the present invention. The unique design features of the present design, taken in combination, make it an improvement on the technology for LTA craft, hybrid LTA craft, and fixed wing flying bodies, especially as applied to unmanned vehicles.

The aircraft has a flexible envelope with a variable rigid inner structure. The envelope has internal bladders adapted to contain low-density buoyant gas. The gas is preferably Helium, however any low-density gas known to a person having ordinary skill in the art is considered. The novel structure includes a central, tube shaped core or cores (depending on size and mission requirements) containing a ducted fan motor, preferably electric, to which all of the other elements electrically attach (power, payload and craft structure). The core(s) use a dual outrigger configuration to support the leading and trailing edges. The two outriggers are generally parallel to the core and attach at the end of the leading and trailing edge members. The outriggers provide structure as well as the mounting for the moveable longerons. The longerons are articulated to adjust the camber and thickness of the aircraft based on flight needs by chamber adjustment assemblies (also referred to as translation assemblies) preferably mounted above and below the core of the aircraft. Payloads are mounted internally to the sides of the core and/or to the translation assembly. This unique structure presents a design that can achieve a range of performances in altitude, payload, and airspeed at a far lower cost and complexity than any existing aircraft of any class.

When the aircraft converts to an LTA configuration—a large buoyant shape, the craft has all of the traditional characteristics of a blimp or rigid airship for station keeping or slow speed flight. By adjusting the shape the lower surface to achieve an airfoil shape, the craft can augment the buoyancy by creating aerodynamic lift to increase its duration of flight. Finally, by reshaping both the upper and lower surfaces, the craft can achieve a relatively low drag configuration for high velocity (in excess of 200 km/hr) to rapidly reposition itself or fly high velocity missions. In a certain embodiment, the design includes a leading edge shield to protect the envelope in high velocity flight.

Example of the Present Invention

As shown in FIG. 1, a certain embodiment of the present invention, generally denoted by reference numeral 100, includes flexible envelope 122 with movable longerons 102, 104. The hybrid LTA 100 has two moveable upper longerons 102 and two moveable lower longerons 104. The movement of the longerons adjusts the camber and thickness of the upper and/or lower surfaces to achieve differing body shapes. The longerons are non-linear, preferably having an arc shape, and preferably having a fixed length to decrease complexity of the aircraft, however length-adjusting longerons are considered. The length of the longerons extends preferably in a direction generally parallel to the longitudinal axis of the aircraft.

The movement of the longerons and therefore camber-transformation can be accomplished while the craft is airborne and does not require any ground support equipment. The transformation changes both the lift and drag characteristics of the craft to alter the flight characteristics. In a certain embodiment, only the upper or only the lower longerons are moveable to decrease complexity and weight of the aircraft.

Moveable upper longerons 102 and moveable lower longerons 104 are each in communication with upper translation assembly 106 and lower translation assembly 107, respectively. The translation assemblies each include motor 108 (See FIGS. 16-21), gear assembly 110, and extendable arms 112. When the translation assembly is in a fully extended configuration, the moveable longerons are in a generally vertical orientation, as shown in FIGS. 1 and 17A, which increases the camber and affects the lift and drag characteristics of the aircraft. When the translation assembly is in a retracted position, the moveable longerons are pulled inwards towards the longitudinal axis of the aircraft, as shown in FIGS. 2 and 17B, which decreases the camber and thickness.

The additional structural components contributing to the present invention's superior functionality include cylindrical core 114 extending the length of the aircraft in the longitudinal direction. Surrounding the core is a rigid, preferably rectangular, base structure comprising leading and trailing edge struts 116 connected to port and starboard outriggers 118. The design also includes envelope expansion arms 120 having an adjustable length and a generally arc shape. There is preferably one envelope expansion arm along the port side of the aircraft and one along the starboard side of the aircraft where each is capable of extending outward away from the central longitudinal axis of the aircraft to alter the span of the aircraft. Enclosing the base structure, envelope expansion arms, and longerons is flexible envelope 122.

Also provided in FIG. 1, is flight stability and control components—elevons 124, vertical stabilizer 125, rudder 126, leading edge shield 127, and propulsion system 128. Pitch and roll control is preferably provided by a pair of rear mounted elevens 124. These devices perform the function of both elevators and ailerons to control pitch and roll respectively. Both are controlled via servos and a microprocessor mounted to the core assembly. Yaw control is provided through rudder 126 mounted to vertical stabilizer 125 as in many conventional aircraft. Vertical stabilizer 125 provides directional stability. Rudder 126 is preferably configured to project into the ducted fan airstream to provide a degree of thrust vectoring for very low speed flight and low velocity maneuvering. It is envisioned that the larger sizes of this LTA would employ thrust vectoring entirely as its method of directional control for certain applications. Thrust vectoring with multiple motors and larger sizes would significantly reduce the weight of the aircraft and provide superior maneuvering capability over conventional control surfaces.

The moveable longerons, envelope expansion arms, and flexible envelope allow the present invention to operate in various configurations. As shown in FIGS. 1, 4, and 5, the aircraft can be configured in a symmetric buoyant configuration, as is typical for LTAs. This configuration includes both upper translation assembly 106 and lower translation assembly 107 in the fully extended position to place moveable upper longerons 102 and lower longerons 104 in a generally vertical orientation. The non-linear arc shape of the longerons increases the thickness of the aircraft when in a more vertical orientation. In addition to the symmetric buoyant configuration, the aircraft can achieve a negative lift configuration, as shown in FIG. 2, by retracting upper translation assembly 106 and extending lower translation assembly 107. Likewise, the aircraft can achieve a positive lift configuration, as shown in FIG. 3, by extending upper translation assembly 106 and retracting lower translation assembly 107. The truly innovative and functionally distinct orientation found in no other LTA to HTA convertible aircraft, is the dash configuration. As shown in FIGS. 5 a and 5 b, the dash configuration is a symmetric HTA configuration achieved when both upper translation assembly 106 and lower translation assembly 107 are in the retracted position. Note that the position of the Longerons is not limited to these two positions, fully extended and fully retracted, but can be configured in any state of extension to achieve optimal aerodynamic performance.

The dash configuration is unique for a partially rigid LTA aircraft. Since the envelope must be flexible to accommodate the shape morphing capability and have very low permeability to Helium while being lightweight, the envelope is preferably made from a plastic sheet material. This material is prone to two negative features that will affect the performance of the LTA in the dash configuration and impact performance overall. One is flutter of the envelope, increasing drag and causing aerodynamic instability. The second is the possibility of penetration of the envelope by airborne hazards (such as insects, birds, debris) at the high speeds. The possibility of penetration is avoided by the installation of leading edge shields that are hinged on the leading edge strut and can expand or contract with the movement of the envelope. Additionally, mechanical stops can be installed to reflect the shape of the leading edge in the dash configuration to remove the possibility of flutter at high speeds.

Aircraft Performance

Due to the variable geometry of the aircraft, it will have a range of performance characteristics from that of a high Coefficient of Drag (CD) dirigible performance to a relatively low CD flying wing configuration. The lift characteristics will also vary from a lift neutral symmetric configuration to a positive lift or negative lift airfoil shape to suit mission requirements. These configurations can be changed dynamically while airborne to suit mission needs. The driving requirement for the device is the desired dash speed of approximately 200 kts. The assessment of performance and structural characteristics has been completed for three different configurations of craft defined by the length or chord of the aircraft and the span of the central, airfoil shaped portion of the craft or span, which excludes the half blimp shape on each end of the craft.

Dash Speed Calculation:

A novel characteristic of this aircraft is the speed at which the aircraft is capable of traveling when in the dash configuration. The equation in Table 2 is used to calculate the amount of force required to move a body through a viscous medium. This is used to derive the motor size to achieve the required speed; thus driving other factors such as weight, power, envelope size etc. The initial calculation is to determine the minimum motor output required to achieve the desired maximum dash velocity of 230 mph at a cruise altitude of 10,000 ft. MSL. Using the desired dash speed shown in Table 2 below, the resultant drag force or the required motor output to overcome that drag is determined. Using a mathematical simulation tool (SimFoil) available from NASA, the CD for various configurations of the aircraft from a large chord to length ratio to a small chord to length ration is calculated. As seen in Table 3, the drag force exhibited by a low chord to length ratio with a highly symmetric profile yields the lowest CD and therefore, the lowest motor size to achieve the desired speeds. The model output corresponding to this performance is shown in FIG. 7. These values are highlighted in the Drag Coefficient section of Table 3 for each of three configurations shown in FIGS. 6, 7, and 8. Also highlighted in the Drag Force and Required Motor Output sections of Table 3 are the best performance conditions for the LTA dash mode. It is apparent that the maximum LTA speed in the highly buoyant configuration (high thickness to chord length ratios) will be nowhere near those achieved in the dash configuration. FIGS. 6 and 7 show the output for two of the symmetric configurations examined using the FoilSim simulation program. FIG. 8 shows how CD increases in the asymmetric configuration while also experiencing a corresponding increase in the coefficient of lift (CO). This case shows that in this configuration, significant aerodynamic lift can be achieved by this design at 0 degree AoA. Higher lift performance can be achieved at higher AoA.

TABLE 2 Desired speed in knots: 200 kys = 102.88 m/sec Fr = .5(C_(D))*ρ_(air)*v²*A_(s) Assume Altitude of 10000 ft and Speed of 250 kts Altitude 10000 ft = 3048 m Speed: 230 mph = 200 kts = 370 km/hr 102.88 v Velocity (m/Sec): in this model, this is an input characteristic and drives the motor size.  0.4135 ρ_(air) Density of Air: is a function of atmospheric conditions and varies as shown in Table 1 Table A Surface Area (m²) Table C_(D) Coefficient of Drag: using FoilSim III

TABLE 3

Propulsion System

The motor size and number of motors are derived for each of the three configurations to determine if commercially available Electronic Ducted Fan (EDF) motors can be used in the design. The data in Table 3 proves that a single 3000 gmf motor is sufficient to achieve the desired velocity for the 1-meter-by-1-meter configuration. This size motor is readily available for Radio Control (RC) aircraft. For larger size craft, the number of core units would be increased to provide the required thrust. This assessment shows that two core units of roughly the same size as above will propel a 2-meter-by-2-meter design. Larger motors or core combinations of four motors would be required for the 4-meter-by-4-meter design, but still feasible. In a certain embodiment, any number of motors and any type of motors may be used as is known to a person having ordinary skill in the art.

Envelope

In a certain embodiment, the envelope is comprised of an outer gas containment bag (or envelope), internal reinforcement layer and a secondary containment bag to facilitate Helium recovery. With elements of the LTA structure movable, there is a concern that structural members rubbing on a fairly thin plastic surface could contribute to failure of the envelope. Therefore, a certain embodiment includes reinforcement layers 130 located in areas likely to experience increased wear and tear from the moveable internal structure of the aircraft. FIG. 9 illustrates the approximate areas on envelope 122 requiring the addition of reinforcement layers 130, likely made of Mylar or some other wear resistant, lightweight, and flexible material, to increase the serviceable life of the envelope. In a certain embodiment, the reinforcement layer is also added at the leading edge and under the translation assemblies to improve tear resistance at possible impact areas from outside debris.

FIG. 10 shows internal panels that will create separate gas bladders within the envelope. The internal panels act as flexible walls creating four independent chambers. The internals panels include top panel 131, bottom panel 132, starboard panel 133, and port panel 134. Top panel 131 runs between the outriggers and rests on the central core, both of which are not shown to aid in clearly identifying the internal panels. Bottom panel 132 is also runs between the outriggers, but is located under the central core. Both the port and starboard panels 134 and 133 run between the top and bottom longerons on the respective sides of the aircraft. The panels are preferably made from the same material as the envelope, however any lightweight flexible and airtight material, as is known to a person having ordinary skill in the art, may be used. These panels aid in the recovery of the low-density gas used in the LTA configuration without venting to the atmosphere, thus conserving the gas for future use. The partition bladders also reduce the possibility of catastrophic gas loss if the envelope integrity is violated. In conjunction with the individual bladders, the aircraft also includes gas containers sufficient for one or more refills and a gas recovery pump system.

As shown in FIG. 11, the base structure of the aircraft includes a rectangular frame made up of leading and trailing edge struts 116 connected to port and starboard outriggers 118. The structure also includes envelope expansion arms 120, which extend outward from the base structure on the port and starboard sides in a generally planar direction with respect to the base structure. A pair of moveable longerons—one moveable upper longeron 102 and one moveable lower longeron 104, is located on both the port and starboard sides of the aircraft. The longerons 102 and 104 and envelope expansion arms 120 are connected at two structural connection points 136 located on each side of the aircraft where the outriggers and struts are connected. Longerons 102 and 104 are moveable such that the longerons may be retracted in towards core 114 of the aircraft as seen on the port side of the aircraft in FIG. 11. As the longerons retract, slack would be created in the envelop if it were not for the envelope expansion arms. Envelop expansion arms 120, under a constant bias force directed away from core 114, lengthen and extend outward in the direction of the bias force, which in turn keeps envelope 122 taught. The envelope expansion arms increase the span of the aircraft as seen in FIG. 5 c.

FIG. 11 also illustrates, on the starboard side of the aircraft, the orientation of longerons 102 and 104 and envelope expansion arm 120 representative of the translation assemblies in the expanded configuration. This configuration includes longerons 102 and 104 in a generally vertical orientation, which results in the envelope forcing envelope expansion arm 120 towards core 114 to overcome some predetermined amount of bias force.

In a certain embodiment, as shown in FIG. 12, the base structure may include an additional support member 138. Support member 138 is included to increase the rigidity of the base structure and may be connected to the base structure at any location known to a person having ordinary skill in the art, such that the structure improves rigidity. Additionally, the base structure would include support structure 138 on both the port and starboard sides of the aircraft.

Also illustrated in FIG. 12 is the open space between core 114 and outrigger 118. This open space allows for the storage of the additional systems that will likely be used in operation. The additional systems are preferably mounted to the sides of core 114, including but not limited to the batteries, computation devices including the navigation system, control computer, battery charge and control device, navigation, servo motors, internal payload elements and structural components for the envelope.

FIG. 13 illustrates a certain embodiment of structural connection points 136. The embodiment shown lacks a connection for an additional support member. The connections of moveable longerons 102 and 104 and the connection for envelope expansion arm 120 are pivoting connections, preferably ball joints, while strut 116 and outrigger 118 connections are preferably fixed connections. The pivoting connections for moveable longerons 102 and 104 and envelope expansion arm 120 aid in the convertibility of the aircraft. The fixed connections of strut 116 and outrigger 118 aid in providing a rigid structure to improve the aircraft's ability to operate under the typical forces and stresses associated with flight. In a certain embodiment, the connection for envelope expansion arm 120 will be spring loaded to produce tension on envelope expansion arm 120 in turn transferring the tension onto the envelope; thereby removing slack in the dash configuration.

As shown in FIGS. 14A and 14B, a certain embodiment has strut-core connection points 140 that pivotally connect struts 116 to core 114. Along with pivoting core-support member connection points 137, strut-core connection points 140 allow the base structure of the aircraft to fold to a more compact orientation and improve transportability of the aircraft. FIG. 14 also illustrate how a certain embodiment includes outrigger-support member connection points 139 instead of the support member connection at the structural connection point. In a certain embodiment, connection point 139 is slidable along outrigger 118 to aid in folding the aircraft.

FIG. 15 provides a certain embodiment of envelope expansion arm 120. The port and starboard envelope expansion arms help set this design apart from all other aircrafts. On the smaller sized aircraft, Carbon tubes of the appropriate diameter telescope to permit the slack in the flexible envelope to be removed so that high dash speeds can be achieved with minimum envelope flutter. The tension will be provided by spring loading features on the structural connection points 136 that connect envelope expansion arms 120, as discussed above.

On larger versions, the telescoping tube design will likely be less effective than the use of a unique anisotropic beam design used to both provide tension on the envelope and to maintain the leading edge shape of the wing extensions. This design is detailed in FIG. 15 and includes two or more composite rods (preferably a three-rod configuration) with spring steel cross members embedded into the structure. The spring constant (controlled by material and length) will be varied across the length of the beam to provide variable tension on the envelope, tailoring the pressure on the envelope depending on aerodynamic conditions. One of the composite rods will interface with the pivot joint assembly at both ends to provide the source of the tension while the other rod(s) will be anchored against the pivot structure. Any twisting or translation of the rods relative to each other, causes the spring steel cross members to attempt to restore the structure to equilibrium. The design allows different spring constants to be used along the length of the structure by adjusting the stiffness and lengths of the cross members so that pressure on the envelope at the tips and trailing edge can be significantly reduced while pressure at the leading edge can be maintained. This feature provides superior tension control with a lightweight structure and significantly reduces envelope flutter in the dash mode.

The cross section of envelope expansion arm 120 is preferably triangular in shape with two rods 144 fixed to cross member trusses (made up of cross members 142) and a third rod 144 slidably attached to the cross member trusses. This unique assembly provides envelope expansion arm 120 with varying length capabilities while also allowing for varying structural support depending on the strength of the individual cross member trusses located along the length of envelope expansion arm 120.

FIG. 16 provides a certain embodiment of upper translation assembly 107. Upper translation assembly 106 includes motor 108, gear assembly 110, and extendable arms 112. In a certain embodiment, the center of gear assembly 110 is attached to the envelope to aid in maintaining proper envelope positioning. As shown in FIG. 17A, extendable arms 112 are attached to upper moveable longerons 102 and when upper translation assembly 106 is in the extended configuration, upper moveable longerons 102 are in a generally vertical orientation. Contrastingly, FIG. 17B shows upper translation assembly 106 is in the retracted configuration, which pulls moveable longerons 102 towards motor 108 and into more of a horizontal configuration.

In a certain embodiment, translation assemblies 106 and 107 have payload hard points 146. Most commonly, the hard point would be located on the lower translation assembly. FIGS. 18 and 19 show lower translation assembly 107 with hard points 146, while in the extended orientation and FIGS. 20 and 21 show the translation assembly in the retracted configuration. Payload hard points 146 provide an attachment structure for securing payloads to the aircraft. In a certain embodiment, payload hard point 146, on lower translation assembly 107, is externally located with respect to the envelope. In this embodiment, extendable arms 112 are in communication with lower moveable longerons inside of the envelope while payload hard point 146 extends downwards and out of the envelope allowing certain payloads to be attached externally of the envelope for certain mission requirements.

In a certain embodiment requiring extended on station performance, the aircraft is equipped with flexible solar panels mounted to the upper exterior surface of the envelope. This allows the aircraft to remain in the LTA configuration and hover while the system batteries are recharged. Energy recovery through the motor is also available while in buoyant mode if turned into the oncoming airstream.

The advantages set forth above, and those made apparent from the foregoing description, are efficiently attained. Since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention that, as a matter of language, might be said to fall therebetween. 

What is claimed is:
 1. An aircraft comprising: a convertible design having a lighter-than-air configuration and a heavier-than-air configuration; a propulsion system; a flexible envelope that encloses a base structure, moveable longerons, and a length-adjusting envelope expansion arm; the moveable longerons in communication with the flexible envelope and in communication with a translation assembly, the translation assembly having an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the moveable longerons are in a low camber orientation, in transitioning to the retracted configuration, the translation assembly moves the moveable longerons inward towards a central longitudinal axis of the aircraft to decrease aircraft thickness, and in transitioning to the extended configuration, the translation assembly moves the moveable longerons outward away from the central longitudinal axis of the aircraft to increase the aircraft thickness; the length-adjusting envelope expansion arm further including: a bias force applied to the envelope expansion arm attempting to force the envelope expansion arm outward in a direction away from the central longitudinal axis of the aircraft; communicating with the flexible envelope; a retracted position and an expanded position, wherein the arm is capable of transitioning between the retracted and expanded positions, in the retracted position, the length of the envelope expansion arm is at a minimum and in the expanded position, the length of the envelope expansion arm is at a maximum; the retracted position is achieved when a tension force in the flexible envelope overcomes the bias force, resulting from the transition of the moveable longerons towards a more vertical orientation, thereby reducing the length of the envelope expansion arm; and the expanded position is achieved when the tension force in the flexible envelope is overcome by the bias force, resulting from the transition of the moveable longerons to a more horizontal orientation, thereby increasing the length of the envelope expansion arm.
 2. The aircraft of claim 1, wherein the moveable longerons further include: upper longerons having a generally arc shape and in communication with the flexible envelope and an upper translation assembly, the upper translation assembly having an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the upper moveable longerons are in a low camber orientation, in transitioning to the retracted configuration, the upper translation assembly pulls the upper moveable longerons inward towards a central longitudinal axis of the aircraft to decrease aircraft thickness, and in transitioning to the extended configuration, the upper translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the upper moveable longerons in a more vertical orientation, which increases the aircraft thickness, compared to longeron's orientation in the retracted configuration; and lower longerons having a generally arc shape and in communication with the flexible envelope and a lower translation assembly, the lower translation assembly having an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the lower moveable longerons are in a low camber orientation, in transitioning to the retracted configuration, the lower translation assembly pulls the lower moveable longerons inward towards a central longitudinal axis of the aircraft to decrease aircraft thickness, and in transitioning to the extended configuration, the lower translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the lower moveable longerons in a more vertical orientation, which increases the aircraft thickness, compared to longeron's orientation in the retracted configuration.
 3. The aircraft of claim 2, further comprising a structural connection point, the structural connection point further including: a first fixed connection attached to an outrigger; a second fixed connection attached to a strut; a first pivoting connection attached to one of the upper moveable longerons; a second pivoting connection attached to one of the lower moveable longerons; and a third pivoting connection attached to one of the envelope expansion arms.
 4. The aircraft of claim 2, wherein the upper and lower moveable longerons each include a port side longeron and a starboard side longeron, wherein each longeron has a predetermined length that extends in generally the same direction as the central longitudinal axis of the aircraft.
 5. The aircraft of claim 1, wherein the envelope expansion arm is an anisotropic beam including two or more composite rods with cross members having a predetermined spring constant embedded into the structure, one of the composite rods is pivotally attached to the aircraft and one or more of the composite rods is anchored against the pivot structure to provide a source of the tension.
 6. The aircraft of claim 1, further including a span that increases when the envelope expansion arm is in the expanded position and decreases when the envelope expansion arm is in the retracted position.
 7. The aircraft of claim 1, further including two envelope expansion arms, a portside envelope expansion arm and a starboard side envelope expansion arm, wherein each envelope expansion arm has a generally arc shape and an adjustable length in generally the same direction as the central longitudinal axis of the aircraft.
 8. The aircraft of claim 1, wherein the moveable longerons are in a generally vertical orientation when in the high camber position and the moveable longerons are in an acute angle orientation when in the low camber position.
 9. The aircraft of claim 1, wherein the base structure includes a central core running along a central longitudinal axis of the aircraft, a leading edge strut extending in a direction perpendicular to and in communication with the central core, a trailing edge strut extending in a direction perpendicular to and in communication with the central core, a port side outrigger extending in a direction parallel to the central core and in communication with struts, and a starboard side outrigger extending in a direction parallel to the central core and in communication with struts
 10. The aircraft of claim 1, further comprising a gas storage and retrieval system adapted to house, distribute, and retrieve lighter-than-air gas.
 11. The aircraft of claim 1, wherein the propulsion system further includes an electrical generator system adapted to convert wind energy into electrical energy while the aircraft is in the lighter-than-air configuration.
 12. An aircraft comprising: a convertible design having a lighter-than-air configuration and a heavier-than-air configuration; a propulsion system; a flexible envelope enclosing a base structure, generally arc shaped moveable longerons, and generally arc shaped length-adjusting envelope expansion arms; the base structure is in communication with the moveable longerons and the envelope expansion arms; the moveable longerons further including: upper longerons in communication with the flexible envelope and an upper translation assembly, the upper translation assembly having an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the upper moveable longerons are in a low camber orientation, in transitioning to the retracted configuration, the upper translation assembly pulls the upper moveable longerons inward towards a central longitudinal axis of the aircraft to decrease aircraft thickness, and in transitioning to the extended configuration, the upper translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the upper moveable longerons in a more vertical orientation, which increases the aircraft thickness, compared to longeron's orientation in the retracted configuration; lower longerons in communication with the flexible envelope and a lower translation assembly, the lower translation assembly having an extended configuration where the moveable longerons are in a high camber orientation and a retracted configuration where the lower moveable longerons are in a low camber orientation, in transitioning to the retracted configuration, the lower translation assembly pulls the lower moveable longerons inward towards a central longitudinal axis of the aircraft to decrease aircraft thickness, and in transitioning to the extended configuration, the lower translation assembly pushes the moveable longerons outward away from the central longitudinal axis of the aircraft to place the lower moveable longerons in a more vertical orientation, which increases the aircraft thickness, compared to longeron's orientation in the retracted configuration; the length-adjusting envelope expansion arms further including: a port side envelope expansion arm and a starboard side envelope expansion arm, wherein the adjustable length of each envelope expansion arm is in generally the same direction as the central longitudinal axis of the aircraft; a bias force applied to each envelope expansion arm attempting to force the envelope expansion arm outward in a direction away from the central longitudinal axis of the aircraft; communicating with the flexible envelope; a refracted position and an expanded position, wherein in the retracted position, the length of the envelope expansion arm is at a minimum and in the expanded position, the length of the envelope expansion arm is at a maximum; the retracted position is achieved when a tension force in the flexible envelope overcomes the bias force, resulting from the transition of the moveable longerons towards a more vertical orientation, thereby reducing the length of the envelope expansion arm; and the expanded position is achieved when the tension force in the flexible envelope is overcome by the bias force, resulting from the transition of the moveable longerons to a more horizontal orientation, thereby increasing the length of the envelope expansion arm.
 13. The aircraft of claim 12, wherein the upper and lower moveable longerons each include a port side longeron and a starboard side longeron, wherein each longeron has a predetermined length that extends in generally the same direction as the central longitudinal axis of the aircraft.
 14. The aircraft of claim 12, further comprising a structural connection point, the structural connection point further including: a first fixed connection attached to an outrigger; a second fixed connection attached to a strut; a first pivoting connection attached to one of the upper moveable longeron; a second pivoting connection attached to one of the lower moveable longeron; and a third pivoting connection attached to one of the envelope expansion arms.
 15. The aircraft of claim 12, wherein the envelope expansion arm is an anisotropic beam including two or more composite rods with cross members having a predetermined spring constant embedded into the structure, one of the composite rods is pivotally attached to the aircraft and one or more of the composite rods is anchored against the pivot structure to provide a source of the tension.
 16. The aircraft of claim 12, further including a span that increases when the envelope expansion arm is in the expanded position and decreases when the envelope expansion arm is in the retracted position.
 17. The aircraft of claim 12, wherein the moveable longerons are in a generally vertical orientation when in the high camber position and the moveable longerons are in an acute angle orientation when in the low camber position.
 18. The aircraft of claim 12, wherein the base structure includes a central core running along a central longitudinal axis of the aircraft, a leading edge strut extending in a direction perpendicular to and in communication with the central core, a trailing edge strut extending in a direction perpendicular to and in communication with the central core, a port side outrigger extending in a direction parallel to the central core and in communication with struts, and a starboard side outrigger extending in a direction parallel to the central core and in communication with struts
 19. The aircraft of claim 12, further comprising a gas storage and retrieval system adapted to house, distribute, and retrieve lighter-than-air gas.
 20. The aircraft of claim 12, wherein the propulsion system further includes an electrical generator system adapted to convert wind energy into electrical energy while the aircraft is in the lighter-than-air configuration. 